The present invention generally relates to the production of decorative laminate panels and, specifically, to top-coated overlays used in such production. The invention particularly relates to compositions suitable for use in preparing decorative overlays, to decorative overlays and to methods employing decorative overlays in the production of end-use laminated articles such as furniture and cabinets.
A number of approaches are known for manufacturing decorative laminate panels. For example, "low-pressure" laminate panels are typically produced by applying a resin-impregnated decorative overlay over a self-supporting substrate such as particleboard, plywood, etc. and heating the resulting composite to temperatures ranging from about 100.degree. C. to about 200.degree. C. while applying a pressure ranging from about 250 psig to about 750 psig. "High-pressure" laminate panels can be produced by applying a resin-impregnated decorative overlay over a series of phenol/formaldehyde resin-impregnated kraft sheets and heating the resulting composite to temperatures ranging from about 100.degree. C. to about 200.degree. C. while applying a pressure of at least about 900 psig, and typically ranging from about 1100 psig to about 1500 psig. In another approach, decorative laminate panels are produced by a hot roll lamination method in which a top-coated decorative overlay in roll form is bonded to a substrate (e.g. board) by an adhesive preapplied to either the board or the backside of the decorative overlay. Other methods for producing decorative laminate panels, such as the use of reverse-printed membrane pressable films, are likewise known in the art. The decorative laminate panels produced according to these and other approaches are used for the manufacture of a wide variety of end-use laminated articles, including for example cabinets, countertops, furniture, plaques, marketing displays, automobile components, etc.
The decorative overlays typically used in such laminate panel manufacturing processes include, for example, plastic-film overlays such as vinyl, polyester, polypropylene, acrylic and fluoropolymer films, and top-coated paper overlays. Decorative overlays can be prepared by printing a substrate such as paper or plastic-film with, for example, a solid color and/or a design such as wood-grain design, and applying a coating of a resin-type material, such as a melamine resin, urea-formaldehyde resin, polyurethanes, epoxies, acrylics and other resins, over the substrate or printed substrate. The top-most coating overlying the substrate, generally referred to in the art as a top-coating, is intended to protect the underlying printing and to impart desirable properties to the overlay. Desirable properties include, for example: hardness, toughness, gloss, scratch resistance, abrasion resistance, water-resistance, chemical-resistance, heat-resistance, ultraviolet-resistance (e.g. to fade and/or darkening), gluability, label-releasability and tape-releasability. Industry-standardized specifications for these and other properties of top-coated decorative overlays have been developed. For example, the Kitchen Cabinet Manufacturer's Association (KCMA) provides target specifications for such overlays in ANSI/KCMA A161.1-1990. Another set of specifications is included in Voluntary Product Standards and Typical Physical Properties of Low Basis Weight Paper Overlays published by the Laminating Materials Association as LMA Standard LBW-1-1992.
A number of compositions are known in the art for use in preparing top-coated decorative overlays. For example, a number of known compositions include a cross-linked melamine-based resin. Such cross-linked melamine resins are typically prepared by combining a melamine resin with a cross-linking agent such as a polyol and a catalyst in an appropriate solvent. Additives such as waxes (e.g. teflon, carnauba) and/or silicones are reported as being combined therewith to impart desirable properties to the resulting top-coating.
While the decorative overlays based on such compositions would preferably possess all of the desired properties to a satisfactory degree simultaneously, known overlays more typically possess desired properties to varying degrees with trade-offs made between two or more desired properties. For example, there is a need in the manufacturing of end-use laminated articles for decorative laminate panels that have an exposed top-coated-decorative-overlay surface which can be glued or bonded to another component of the article. Additionally, because such articles are typically sold with pressure-sensitive labels and/or tape applied to their surfaces and because such articles are often subjected to repeated applications of pressure-sensitive tape to their surfaces when in use (e.g. masking tape applied to cabinets for painting purposes), there is also need for a decorative overlay having a top-coated surface which allows for release of labels and/or tape without damage to the surface. However, decorative overlays known in the art have not, heretofore, simultaneously satisfied both of these needs.